Electric valve translating apparatus and method of operation



Oct. 2, 194.5.F A. H. MrrTAG ETAL ELECTRIC VALVE TRANSLATING APPARATUS AND METHOD OF OPERATION Filed June lel 1943 (pija,

Attopey.

Patented Oct. 2, 1945 ELECTRIC VALVE TRANSLATING APPA- RATUS AND METHOD F OPERATION Albert H. Mittag and August Schmidt, Jr., Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application June 1s, 1943, serial No. 490,996

(ci. :ils- 266) 5 Claims.

This invention relates to electric valve translating apparatus and more particularly to an improved method and apparatus for placingA a plurality of parallel connected electric valve units in operation.

Electric valve systems employing a number of units operated in parallel have been widely used as a power supply for electrolytic processes requiring currents of large magnitudes. Some difficulty has been experienced in placing apparatus of this character in operation due to failure of all of the electric valves of the apparatus to become conductive at the intended time. The electric valves which conduct first temporarily assume all of the load which, in many cases, is suilicient to operate the protective equipment and isolate the overloaded unit or units. Some of the discrepancy in starting time among the various parallel units may be due to failure of the system provided for energizing' the control members of the electric valves to render the electric valves conductive at sumc-iently near the same instant. In installations employing electric valve means having starting electrodes of the make-alive type, at least a part of the discrepancy in starting time of the various units has been found to result from failure of the starting electrodes to form a cathode spot regularly for a considerable interval after the first energlzation thereof. In accordance with the teachings of this invention,v there is provided an improved circuit and method of operating the same which insures a more uniform v assumption of load by the various parallel operating units.

Itis an object of this invention to provide new and improved electric valve translating apparatus.

Itis another object of this invention to provide a new and improved control means for controlling the operation of a plurality of electric valve units in parallel and to provide an improved methodof placing suchapparatus in operation. v

' to the starting electrodes to bring the starting electrodes to operating temperature. A negative bias is then impressed on the control members or grids and all of the power circuit breakers interconnecting the supply and load circuits and the electric valve units are closed. after the starting electrodes have been energized for an interval of a minute or two to insure that they are at an operating temperature which insures `reliable operation, the negative bias is removed from the control members of all of the electricvalve units by means of a single switch which short circuits the source of negative `bias through a current-limiting resistor. Relay means are provided for transferring the neutral connections of the excitation transformers associated with the control members of each of the valves from the common source of bias back to the respective cathode buses of the individual units. 'I'he short-circuiting switch may then be opened and the source of bias deenergized if desired to place the system in condition for another starting operation. With this apparatus and the method of operating it, the assumption'of load by the individual units is suiliciently uniform to insure ,trouble free starting of the system.

I'his invention will be better understood by reference to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. In the drawing, the single figure illustrates schematically one embodiment of our invention. y .i l In the arrangement shown in the drawing, a pair of electric valve rectifying units i0 and li are shown connected in parallel between a threephase alternating-current supply circuit l2 and a direct-current load circuit comprising conductors I3 and i4. It will be understood that the present invention is particularly adapted for use in connection. with a system employing a large number of rectifier units in parallel but, in orderr to simplify the drawing, only two of the units have been illustrated. The rectifier unit i0 .comprises a supply transformer I5 having a preferably of the type employing an ionizable medlum. such as a. gas or vapor. and, 'as illustrated,

fying unit II is in general the same as the electric valve rectifying unit III except that the voltages impressed on the anode-cathode circuits of the electric valves thereof are displaced in phase with respect to the voltages of the unit I0 by the supply transformer 23 which includes a Y-connected primary winding 30 and electrically displaced secondary windings 3I and 32. The remainder of the unit II is of thesame arrangement as the unit III and the same reference numerals have been employed to designate corresponding parts. Only two electric valves have been illustrated in connection with the units I0 and II in order to simplify the drawing. It will be understood that a similar electric valve and circuit breaker interconnect each'of the phase terminals of the transformer secondaries and the respective cathode buses 2U.

In order to energize the starting electrodes 25 with periodic voltagesof peaked wave form, there have been illustrated static impulsing circuits of the type described and claimed in the copending application of Alexanderson and Mittag, Serial No. 374,716, iiled January 16, 1941, entitled "Electric control circuits, and assigned to the assignee of the present application. As illustrated.' eachl of the excitation circuits 33 and 34 comprises a capacitance k35 which is arranged to be charged from one phase of an alternatingcurrent excitation bus 33 through suitable phaseshifting means 31 and a charging impedance, such as a reactor 33. As illustrated, the bus' 36 is energized directly from the supply circuit I2.`

The discharge circuit for the capacitance includes an auto-transformer 39 having a midtap connected with the cathode bus and with the end vterminals connected with the control electrodes oi. electric valve means 2I associated with phaseterminals of the supply transformerl windings which are electrically displaced 180 electrical degrees. The circuit of each of the control electrodes preferably includes a unilaterally conducting device 4Q to prevent reverse current from traversing the control electrode. The discharge of the, capacitance through the autotransformer 33 and the control-electrode-to-cathode circuits cf the electric valves 2l is controlled by a self-saturating reactor 4I connected in the discharge circuit of the capacitor 35. The reactor 4I is of the self-saturating type and the impedance thereof reduces abruptly at a predetermined point in the voltage wave impressed thereon by capacitor 35, thus producing symmetrical voltage peaks across the autctransformer 39 during both positive and negative half cycles. 'A unidirectional winding 42 may be provided and may be energized from a suitable source of direct current, not shown, to render the peaks symmetrical with respect to the positive-Tand negative half cycles,' inf-forA any reasonf the instantsfofselfsaturation' farefnot exactly symmetrical. f-

ductor 53.

In ardente-assist lal-thapropagationcfthefarc from fthe cathode/l `-i'l'inied .by -the starting electrodes 2l.: there-'ia' provided meanaf for im.-

pressing fair.l alternating-f voltage fon-1 the control members 23 having a suitable phase relation with respect to the alternating-current supply voltage. Associated with each of the units I0 and II is an excitation transformer 43 having a delta-connected primary winding 44 energized from the alternating-current supply circuit I2 through suitable phase-shifting means illustrated schematically at 45. The secondary winding 46 of the transformer is preferably a. 'diametric sixphase winding providing six phase terminals, one for each control member of each of the rectifier units. Only the control member 'of one of the electric valves of each unit is shown connected. The neutral 'of the transformer winding 46 is arranged to be connected with the cathode bus 20 of the rectifier unit I0 under the" control of the contact 41 of an electromagnetic relay` 48 or to the negative direct-current line I4 through the contact 50 of an electromagnetic relay 5I, a current-limiting resistor 52 and a source of negative-biasing potential which may be impressed between the conductor I4 and a con- As illustrated in the drawing, the negative-biasing potential may be obtained from the alternating-current source by means of a rectifier circuit including a transformer 54 and a polyphase rectiiier connection employing a plurality of rectiiiers 55, preferably of the dry type. The output of the rectifier circuit is impressed across a capacitor 5B and the contacts 51 and 53 of a relay 59 through a resistor 60. In the closed position of the relay 59, then contacts 51 and 58 are connected with the-conductors 53 and I4, respectively. The primary winding of the transformer 54 may be energized from the alternating-current supply circuit I-2 though a three-pole electromagnetic switch 6I including.

an operating coil 62. As a source of energizing potential for relays I4t, 5I, 59', and coil 52, there is provided a single-phase auxiliary alternatingcurrent circuit 63 which may be energized from any suitable source, such as supply circuit I2. The coil 62 and the coil 64 of the relay 59 are connected in parallel for energization -from the circuit 33 under the control ofa manual switch 55. Relays 3l and 5I are interlocked so that one is energized when the other is deen'ergized and vice versa. Referring particularly to the circuits of these relays associated with the rectiiier unit Il), the operating coil of relay 48 is connectedv across the single-phasecircult 53 through a normally closed contact 31 on the relay 5I and the operating coils 58 of relays 5| of units Ill and II are connected in parallel and across 'the alternating-current supply circuit 33 through the normally open contact 63 of a relay 10. The relay 10 is provided with an operating coil 1I which is energized from the circuit 33 through a transformer 12 with a manual switch 13.

The features and advantages which characterize the' present invention will be better understood by a brief consideration of the operation of the system and particularlythe method of placing rthe system in operation. First the alternating-current circuits I2 and 53 are energized by closure of the appropriate switches (not shown). When the circuit I2 is energized, the excitation circuits 33 and 34 are energized to transmit impulses of current to the starting electrodes 25 at the periodicity of thel voltage of the alternatingcurrent supply circuit and at a phase position with respect to the anode-cathode voltages dependent upon the setting of the phase-shifting assaoes 3 energizes the relays 4l and connects the neutrals of the transformer secondary windings 45 directly with the cathode buses 20 of the respective units I and ii. Next the switch 13 is closed to pick up the relay 'l0 which, by closure of its contact 59, 5-

energizes the operating coils of the relays 5I associated with all of the rectifier units. Opening of the contacts 51 of the relays 5| deenergizes the operating coils 56 of the relay 48 to transfer the neutral connection of the respective transformer 10 windings 46 from the individual cathode buses 20 to the common conductor 53. Next the switch 55 is closed to energize the operating windings of switch '6I and relay 59 to energize the bias rectifier circuit and to close the relay 58 to impress the 15 output of the bias rectifier between the conductor 53 and the conductor I4. The conductor 53 is connected with the `respective neutrals of the transformer windings 46 through resistors 52 and1 contacts 50 of relays 5i which are now in the 20 closed position. The system is now ready for closure of the power breakers as soon as the starting electrodes have been energized for a suillcient period to bring them to a good operating,v

temperature. After closing all of the power 25 breakers 22, 2l, and 28 of all of the parallel units,

v the negative bias is removed simultaneously from theneutral connections of all of the transformer windings 46 by closing the single contact of a shorting switch 14 across the conductors I4 and 30 5I. This removes the negative bias from all of the control members 25 at the same instant and, with the starting electrodes 25 all in operating condition, starting of all of the electric valves at the intended instant is assured. With the system now yin operation, switch 1l is opened to deenergize 'relay 5| and energize relays 4l to transfer the neutral connections of the transformer windings from the conductor 53 back to the respective buses 20 of the individual recti- 40 iler units. Switch 65 is opened to deenergize the bias source and switch 14 may be opened to place the system in readiness for another starting operation after a shutdown.

The system described above may be employed 45 to place in operation a plurality of parallel connected electric valve units without the use of the single snorting switch. When used in this manner, the valve units are placed in operation by opening the switch 13 to deenergize relays 5I and 50 energize relays- 48 to transfer the neutral connections of the excitation transformer windings 46 from the conductor 53 to the cathode buses 20.

However, in the operation of the system in this manner, the removal of the negative bias is accomplished by the dropout of a plurality of relays which may not in all cases occur with the degree of simultaneity required for satisfactory pickup of the load current by the parallel units.

From the foregoing description, it is apparent that the present,y invention provides a system and method for placing a plurality of parallel electric I valve units in operation and in which discrepancies in the starting of the 'individual electric valves due to failure of the electrodes to form a cathode spot during the ilrst cycles that they are energized or by failure of the control member excitation system to release the electric valves at the same instant are eliminated.

While there has been shown and described a particular embodiment of this invention, it will be .obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and it is, therefore, aimed in the appendedy claims to fof electric valve means connected between said circuits, each of said valve means comprising an anode, a pool-type cathode, a make-alive starting electrode, and a control member interposed between said anode and said cathode, means connecting the cathodes of said electric valve means to one side of said direct-current circuit, excitation circuits for supplying electrical impulses to said starting electrodes at the periodicity of said alternating-current circuit to form periodically cathode spots, a plurality ofv excitation transformers arranged one with each of said groups of electric valve means and each having a winding including phase terminals connected with the control members of its associated group of electric valve means for impressing an alternating voltage thereon and a neutral terminal, a conductor common to the neutral terminals of all of said excitation transformers, means including a source of unidirectional voltage for impressing between said conductor and all of said cathodes a unidirectional voltage with said conductor having a negative polarity, means connecting the neutral terminal of each of said transformer windings and said conductor to impress a negative bias voltage on said control members to maintain said valve means nonconductive while said starting electrodes are energized, and a single switching means for short circuiting the cathodes of said electric valve means to said conductor to remove said unidirectional voltage simultaneously from ail of said control members.

2. In combination, an alternating-current circuit, a direct-current circuit,` a plurality of tween said circuits, each of said valve means comprising an anode, a pool-type cathode, a

make-alive starting electrode, and a control member interposed between said anode and said cathode, means connecting the cathodes of said electric valve means to one side of said directcurrent circuit, excitation circuits for supplying electrical impulses to said starting electrodes at the periodicity of said alternating-current circuit to form periodically cathode spots, an excitation transformer associated with each of said groups of electric valve means and having a winding including phase terminals connected with said control members for impressing alternating voltages thereon and a neutral terminal, means including switching means connecting the neutral terminal of each of said transformer windings with the cathodes of the associated group of electric -valve means, a conductor, means for impressing between said conductor and all of said cathodes a unidirectional voltage with said conductor having a negative polarity, switching means connected between a5 the neutral terminal of each of said transformer windings and said conductor so that when said first-mentioned switching means are in an open position and said last-mentioned switching means are in a closed position a negative bias voltage is impressed on said control members to maintain said valvemeans nonconductive, means for short circuiting the cathodes of said electric valve means to said coni ductor to.v remove said unidirectional voltage 76 from all of said control members simultaneeach positive anode cycle of ously, and means for opening said last-mentioned switching means and closing said ilrstmentioned switching means to exclude said conductor from the circuit of the control members.

3. In combination, an alternating-current circuit, a direct-current circuit, a. plurality of groups of electric valve means connected between said circuits, each of said valve means comprising an anode, a cathode, and a control member interposed between said anode and said cathode, means for establishing electron emission from each of said cathodes periodically in each positive anode cycle of its associated anode, means connecting the cathodes of said electric valve means to one side of said direct-current circuit, a plurality of excitation transformers arranged one with each of said groups of electric valve means and each having a winding including phase terminals connected with the control members of its associated valve group for impressing an alternating voltage thereon and a neutral terminal, a conductor common to the -neutral terminals of all of said excitation transformers, means including a source of unidirectional voltage for impressing between said conductor and all of said cathodes a unidirectional voltage with said conductor having a negative polarity, separate meansv associated with each neutral terminal for interconnecting the neutral terminal of each of said ,transformer windings and said conductor to impress a negative bias voltage on said control members to maintain said valve means nonconductive during an initial period of time sumcient to establish periodic electron emission from the cathodes of all of said valve groups, and a single switching means for interconnecting all the cathodes of said electric valve means and said conductor thereby to by-pass and to remove said unidirectional voltage simultaneously from all. of said control members after periodic cathode emission has been established for said initial period.

4. In combina-tion, an altemating-current circuit, a direct-current circuit, a plurality of groups of electric valve means connected between said circuits, each of said valve means comprising 'an anode, a cathode, and a control member interposed between said anode and said cathode, means for establishing electron emission from each of said cathodes periodically in its associated anode, means connecting the cathodes valvemeans to one side of said direct-current circuit, a plurality of excitation transformers arranged one with each of said groups of electric valve means and each having a winding including phase terminals connected with said conoi' said electric a,ase',oss

trol members for impressing alternating voltages thereon and a neutral terminal, means including separate switching means associated with each neutral terminal for connecting its associated neutral terminal to the cathodes of the associated group of electric valve means, a conductor com-mon to all of said neutral terminals, means including a single source of unidirectional voltage for impressing between said conductor and all of said cathodes a unidirectional voltage with said conductor having a negative polarity, a separate additional switching 'means connected between the neutral terminal of each of said transformer windings and said conductor so that when said mst-mentioned switching means are in an open position and said lastmentioned switching means are in a closed posi- -tion a negative bias voltage is impressed on said control members to main said valve means nonconductive, while all oi' said cathodes are in an emisslve condition and for a period of time after initiation of said emission and means for opening said last-mentioned switching means and closing said first-mentioned switching means to exclude said conductor from the circuit of the control members to render said valve means conductive at the termination of said period of time.

5. In combination, an alternating current circuit, a direct current circuit, a plurality of groups of electric valves, switching means'having open and closed positions for controlling the connection of said plurality of groups of electric valves in parallel relation between said alternating and direct current circuits, each of said valves comprising an anode, a ,pool-type cathode, a make-alive starting electrode, and a control member interposed' between said `anode and said cathode, a source of negative bias potential, a source of alternating control potential, means i'or connecting said .sources of potential in superposed relation between each control memberand its associated cathode, said negative bias potential being of a. value suiilcient to maintain each valve non-conductive when said switching means is in a closed position and each valve is in a state of ionization for conduction, means for energizing each starting electrode with periodic impulses oi' current to form a cathode spot on its associated cathode, and single switching means for short circuiting said negative bias potential to remove simultaneously the negative bias potential from all said control members to render said valve means conductive after said starting electrodes have been energized a predetermined time.

` AUGUST SCHMIDT, JR.

ALBERT H. MII'I'AG. 

